The present invention relates to spindle motors and disk-drive devices utilizing the spindle motors; in particular to low-profile spindle motors furnished with hydrodynamic bearings, and to disk-drive devices utilizing the spindle motors.
In hard-disk drives that drive hard disks and like recording disks, spindle motors utilizing hydrodynamic bearings that, in order to support the shaft and sleeve as either one rotates relative to the other, employ the fluid pressure of a lubricating fluid such as oil interposed between the two are known.
With regard to spindle motors utilizing hydrodynamic bearings of this sort, the applicant in the present application has proposed, in Japanese Laid-Open Pat. App. No. 2000-113582, a spindle motor as illustrated in FIG. 1. Between the bottom face of a rotor 100 and the top-end face of a sleeve 102 in the spindle motor depicted in FIG. 1, a thrust bearing section 104 is configured. Likewise, between the outer circumferential surface of a shaft 106 furnished integrally with the rotor 100, and the inner circumferential surface of the sleeve 102, radial bearing sections 108, 108 are configured. The thrust bearing section 104 generates lifting force on the rotor 100, and the radial bearing sections 108, 108 function to center-balance in the radial direction, and prevent wobble in, the rotor 100.
The spindle motor depicted in FIG. 1 makes the thrust plate that would be a component of the thrust bearing in conventional hydrodynamic bearings unnecessary. The consequent advantage is a simplified structure that reduces the cost of the motor and at the same time enables it to be slimmed, without appreciably compromising the bearing rigidity. Nevertheless, with the advent of the application of disk drives in miniature devices such as portable information terminals, demands are on the rise to make the spindle motors used in the disk drives even slimmer. In addition, calls for lowering the cost of spindle motors still further have gone hand in hand with reducing the cost of disk drives.
Running counter to this is the fact that in its sleeve 102 the spindle motor depicted in FIG. 1 is provided with a communicating passage 110 made up of a through-hole 110a and channels 110b, 110c. The communicating passage 110 brings outside air into the bearing areasxe2x80x94that is, it enables air to circulate into and out of the bearing areasxe2x80x94and thus making the end portions of the radial bearing sections 108, 108 exposed to the air. Due to the pumping action of dynamic-pressure-generating grooves formed in each bearing section, areas in which the internal pressure of the oil retained among the bearing sections becomes negative, i.e., at pressure less than atmospheric pressure, arise. Upon a decrease in the internal pressure of the oil to a negative pressure level, air that is entrained in the oil during the process of charging the bearing sections with oil, or that is present due to being swept in by the dynamic-pressure-generating grooves, appears in the form of bubbles. The volume of the bubbles expands with increasing temperature or decreasing external environmental pressure. The volume expansion of the bubbles brings leaking oil toward the exterior of the bearing sections and impairs the spindle motor""s durability and reliability. Furthermore, the dynamic-pressure-generating grooves that are formed in the bearing sections come into contact with the bubbles, which causes vibrations and worsens non-repeatable run-out. The rotational precision of the spindle motor therefore worsens. Accordingly, the spindle motor configuration includes the communicating passage 110 in order to exhaust bubbles to the exterior of the bearing sections.
To bore the communicating passage 110 for discharging bubbles in this way a drilling tool is used. The drill bit can only be so small, however, to be strong enough for machining, which limits how small the through-hole 110a and the channels 110b, 110c that constitute the communicating passage 110 can be made. Consequently, the axial dimension of the shaft 106 and the sleeve 102 must necessarily be at least a given size for boring the communicating passage 110 and be extensive enough to maintain bearing rigidity in the radial bearing sections 108, 108. These requirements stand in the way of making the spindle motor slimmer.
What is more, the fact that the through-hole 110a as well as the channels 110b, 110c that constitute the communicating passage 110 are formed in the sleeve 102 complicates that part of the structure and at the same time increases the number of manufacturing processes. An increased-cost spindle motor is the result.
Further still, a ring element 112 that constitutes a retainer for the rotor 100 is fitted onto the end portion of the shaft 106 on the side opposite the rotor 100. In short, because the thrust bearing section 104; the radial bearing sections 108, 108; the through-hole 110a as well as the channels 110b, 110c that constitute the communicating passage 110; and the ring element 112 are arranged in the axial direction stacked along the same axis, they create an impediment to making the spindle motor slimmer.
An object of the present invention is to simplify and slim down the structure of a spindle motor while maintaining its rotational stability.
Another object is in a spindle motor to maintain the internal pressure of the oil retained within the bearing gaps at or above atmospheric pressure, to enable preventing the occurrence of air bubbles within the oil.
Yet another object is balancing the internal pressure of the oil retained within the bearing gaps of a spindle motor.
A different object of the present invention is to enable preventing particulate matter from being produced due to contact between the rotor and stator components in a spindle motor.
Moreover, the present invention provides a low-profile, low-cost disk drive that can spin recording disks stably; and another object of the present invention accordingly is to enable preventing the occurrence of read/write errors that originate in oil leaking out from, or in particulate matter being produced by, the spindle motor in a disk drive device.
One example of a spindle motor under the present invention is configured with a radial dynamic-pressure bearing section, in between the inner circumferential surface of the sleeve and the outer circumferential surface of the shaft, that induces hydrodynamic pressure in oil during rotation of the rotor. On at least either one of the upper-end face of the sleeve, or the bottom face of the rotor, the motor is also furnished with dynamic-pressure-generating grooves, configuring a thrust bearing section, that impart radially inward-heading pressure to the oil during rotation of the rotor. In addition, at its tip end the shaft is configured with an axial support section in which pressure that essentially balances with the oil pressure within the thrust bearing section is utilized.
Likewise, in another example of a spindle motor under the present invention, by a thrust bearing section, radially inward-heading pressure is imparted to the oil during rotation of the rotor; and by a radial bearing section, hydrodynamic pressure having an axially symmetrical pressure gradient is induced in the oil during rotation of the rotor. An axial support section whose pressure essentially balances with the radially inward-heading pressure generated in the thrust bearing section is formed along the end face of the shaft, and by cooperation of the thrust bearing section and this axial support section, the rotor is lifted. A communicating pathway is formed in between the outer circumferential surface of the shaft and the inner circumferential surface of a casing member, for communicating oil retained in, and enabling to circulate between, the thrust bearing section, and the axial support section along the end faces of the shaft and the casing member.
Moreover, in a different example of a spindle motor under present invention, a thrust bearing is configured in between the upper-end face of the sleeve, and the bottom-face of the hub, and a radial dynamic bearing is configured in between the inner circumferential surface of the sleeve and the outer circumferential surface of the shaft. Along its outer circumferential surface the sleeve is furnished with a radially flaring annular flange portion, while on the inner circumferential surface of a round-cylindrical wall on the rotor, an annular member whose surface at least is harder than the sleeve is fixedly fitted. The flange portion and the annular member engage with each other to form a rotor retainer.
In one example of a disk drive under the present invention, the spindle motor that spins recording disks includes: a radial dynamic-pressure bearing section, in between the inner circumferential surface of the sleeve and the outer circumferential surface of the shaft, that induces hydrodynamic pressure in oil during rotation of the rotor; and also a thrust bearing section provided with dynamic-pressure-generating grooves, on at least either one of the upper-end face of the sleeve or the bottom face of the rotor, that impart radially inward-heading pressure to the oil during rotation of the rotor. In addition, at its tip end the shaft has an axial support section in which pressure that essentially balances with the oil pressure within the thrust bearing section is utilized.
Likewise, in another example of a disk drive under the present invention, by a thrust bearing section in the disk drive""s spindle motor for spinning recording disks, radially inward-heading pressure is imparted to the oil during rotation of the rotor; and by a radial bearing section, hydrodynamic pressure having an axially symmetrical pressure gradient is induced in the oil during rotation of the rotor. An axial support section whose pressure essentially balances with the radially inward-heading pressure generated in the thrust bearing section is formed along the end face of the shaft, and by cooperation of the thrust bearing section and this axial support section, the rotor is lifted. A communicating pathway is formed in between the outer circumferential surface of the shaft and the inner circumferential surface of a casing member, for communicating oil retained in, and enabling it to circulate between the thrust bearing section, and the axial support section along the end faces of the shaft and the casing member.
Moreover, in a different example of a disk drive under present invention, the spindle motor that spins recording disks includes: a thrust bearing configured in between the upper-end face of the sleeve, and the bottom-face of the hub; and a radial dynamic bearing configured in between the inner circumferential surface of the sleeve and the outer circumferential surface of the shaft. A radially flaring annular flange portion is furnished on the outer circumferential surface of the sleeve, while on the inner circumferential surface of a rotor round-cylindrical wall, an annular member whose surface is at least harder than the sleeve is fixedly fitted. The flange portion and the annular member engage with each other to form a rotor retainer.